1. Field of the Invention
The present invention generally relates to an endoscope that has an object optical system with a variable focal length at the end of an insertion part. The present invention also relates to an endoscope cap that is fitted on a distal end of an insertion part of a medical endoscope.
2. Description of the Related Art
An endoscope that magnifies a mucous membrane like a microscope can change a depth of focus (observation distance). When a focal length of an object optical system is large, the depth of focus is small. When the object is not completely in the ideal position, it is out of focus.
Japanese Patent Application Laid-open No. 11-342104 discloses a zoom endoscope that has a cap fitted on a distal end of an insertion part to maintain the distance between the object and an object optical system appropriate. The endoscope sets the end of the cap as the ideal focus position for the object optical system, and puts the end of the cap in contact with the mucous membrane to position the mucous membrane at the ideal focus position.
Each of the caps disclosed in Japanese Patent Application Laid-open Nos. 10-248792 and 11-342105 is cylindrically shaped and composed of a peripheral part and an end part. The peripheral part is fitted on the outer periphery of the distal end, and the end part is a predetermined length from the end of the distal end and comes in contact with the object. Since the distance between the object and an object optical system in the distal end is constant, the object optical system can be focused on the object when the predetermined length is appropriately set.
In the zoom endoscope of Japanese Patent Application Laid-open No. 11-342104, however, when the cap is in contact with the mucous membrane, it goes out of focus due to the pulsation motion of the patient and all other movement.
After the cap is fitted, a step is formed between the peripheral part and the end part. Thus, the cap is lodged in the patient""s body when the insertion part is inserted into or drawn from the body, and this may cause pain or discomfort to the patient.
In case of the cap of Japanese Patent Application Laid-open No. 11-342105, there is a large step between the peripheral part and the distal end. The cap is also lodged in the body.
The present invention has been developed in view of the above-described circumstances, and has as its object the provision of an endoscope that can be focused on an object without being affected by pulsation motion of a patient and all other movement.
The present invention has been developed in view of the above-described circumstances, and has as its object the provision of an endoscope cap that does not have a step after it is fitted so that an insertion part of an endoscope can be smoothly inserted into and drawn from a patient""s body.
In order to achieve the above-described object, the present invention is directed to an endoscope with an object optical system that can change a focal length in a distal end of an insertion part, wherein: an ideal focus position for the object optical system is a predetermined length behind of an end of a cap fitted on an outer periphery of the distal end of the insertion part.
According to the invention, the position to which the object swells when the cap is pressed against it is set as the ideal focus position. Thus, the object optical system can be focused on the object without being affected by the pulsation motion of the patient and all other movement.
A section of an edge part of the end of the cap is ark-shaped with the radius of curvature of the predetermined length. The object is not damaged even when the edge part is pressed against the object.
Marks for various magnifications are formed on an inner periphery of the cap. The end of the insertion part is put on one of the marks for a corresponding magnification.
In order to achieve the above-described object, the present invention is directed to an endoscope cap that is fitted on an outer periphery of a distal end of an insertion part of an endoscope, wherein: the endoscope cap is composed of a peripheral part that is on the outer periphery of the distal end and an end part that comes in contact with an object; the peripheral part is thinner than the end part; an outer diameter of the peripheral part is smaller than an outer diameter of the end part before the endoscope cap is fitted; and the outer diameter of the peripheral part is substantially the same as the outer diameter of the end part after the endoscope cap is fitted.
According to the invention, the outer diameter of the peripheral part is smaller than that of the end part before the cap is fitted, and the outer diameter of the peripheral part is substantially the same as that of the end part after the cap is fitted. Thus, there is no step between the peripheral part and the end part, and the insertion part of the endoscope can be smoothly inserted into and drawn from the patient""s body.
In addition, the end part is softer than the peripheral part, and the end part softly comes in contact with the object. Thus, the object is not damaged, even when the end part is pressed against the object. Since the peripheral part is harder than the end part, the peripheral part is firmly fitted on the end of the insertion part.